This invention relates to a direct-current power-supply device for spark erosion machines, arc welding machines or the like.
In general, the circuit of the direct-current power-supply device of the present invention comprises a power transformer for obtaining a large amount of current at a secondary circuit thereof, a thyrister as an element for controlling an output current, and a trigger circuit for controlling the trigger angle of the thyrister.
The circuits of conventional devices have the disadvantage that thyristers used in the circuit frequently break down due to a sudden or rapid change of load, a short circuiting of output-current terminals, or a sharply increased transient current. For example, in an arc welding machine, when the impedance between one electrode and another electrode which is connected to a workpiece rapidly changes, the thyrister has easily broken down.
For the purpose of attempting to resolve the above disadvantages and problems, a reactor has heretofore been connected to the output-current terminal so as to suppress or alleviate the sharp rate of increase of the output-current. However, the employment of a reactor is not sufficient to diminish the rupture of thyristers.
Accordingly, it is an object of the present invention to provide a power-supply device for various kinds of working machines such as spark erosion machines and the like which overcomes the aforementioned disadvantages of prior art devices wherein the circuit of the device of the present invention is constructed and is provided with means employed in the circuit so as to prevent the rupture of the thyrister employed in the circuit and accordingly, working machines are provided with stable output-current.